This weekend, [movie id="291128"]"Where the Wild Things Are"[/movie] finally comes to the big screen after being considered "unfilmable" for decades. But what, exactly, does that word even mean? And with this year's adaptations of "Wild Things" and "Watchmen," does it even still apply?

Below is a list of the books that have given Hollywood headaches for decades. Some have been filmed, some currently linger in development hell, and others will never be touched by any sensible filmmaker. Read on, and ask yourself the two questions that always seem to come up with such projects: "Why not?" or "Why bother?"

"Where the Wild Things Are" (2009)

It's a 20-page book with nine sentences in it. Massive parts of the "plot" are left open with such lines as "let the wild rumpus start!" It features enormous big-nosed monsters, a giant chicken, and a distinctively Sixties state of mind. Thirty-six years after it was first published, all that teeth gnashing has finally yielded a feature film — and if Spike Jonze had never come along, we most likely would have had to wait another generation or two.

"Watchmen" (2009)

It was a groundbreaking graphic novel made specifically to exist in that medium, created by a fiercely brilliant writer (Alan Moore) who despises Hollywood. Its epic nature, cerebral story line and inglorious characters spent decades chewing up would-be adapters like Terry Gilliam, Darren Aronofsky and Paul Greengrass. Earlier this year, the wait finally ended with a blockbuster directed by Zack Snyder that received mixed reviews but a solid box-office return. Arguably, it's the most successful "unfilmable movie" ever made.

"American Psycho" (2000)

Why was this 1991 Bret Easton Ellis novel considered "unfilmable"? Let's just say that all that blood, gore, cannibalism and a climactic scene involving a gerbil pipe and a ravenous rat didn't exactly scream "box-office bonanza." But somehow, Ellis' immensely controversial novel remained relatively intact when it hit the big screen with Christian Bale as ruthless madman Patrick Bateman — and a woman behind the camera. Well-reviewed and regarded by fans, "Psycho" took a chainsaw to the popular theory that mainstream audiences couldn't handle its brutality.

In case you didn't know, Dr. Hunter S. Thompson did a lot of drugs. It made for fascinating prose when mixed with his one-of-a-kind personality, but who would be crazy enough to try and make a movie about the adventures of his loosely autobiographical characters, living a life blurred somewhere in between reality and surreality? Gilliam, Johnny Depp and Benicio del Toro, that's who. Some love the movie, some hate it — but pretty much everyone is still amazed it ever got made.

"Naked Lunch" (1991)

If you think Hunter S. Thompson did a lot of drugs, well, William S. Burroughs made him look like a Girl Scout. That's why the Beat novelist's 1959 semiautobiographical novel about secret agents, extermination, substance abuse and that crazy time Burroughs killed his wife was considered a one-of-a-kind read. That is, until "Eastern Promises" filmmaker David Cronenberg got his hands on it, inserted an impressive array of creepy sci-fi bugs and monsters, and turned the film into a classic on its own merits.

"On the Road" (yet to be filmed)

Arguably the longest-in-development movie of all time, any adaptation of Jack Kerouac's 1957 masterpiece would seem doomed for failure. It's a book about words, of getting into the mindset of a young man in '50s America exploring our country and himself with the help of jazz, poetry, random encounters and lots of mind-altering substances. Still, this hasn't stopped Francis Ford Coppola from spending 30 years grappling with the book's rights — most recently announcing in 2005 that "The Motorcycle Diaries" director Walter Salles would finally film it. We'll only believe it when we see Sal Paradise on the big screen with our own eyes.

"The Catcher in the Rye" (yet to be filmed)

So long as beloved, famously reclusive author J.D. Salinger is still alive, you'll never see Holden Caulfield on the big screen — period. Decades of Hollywood legends from Brando and Nicholson to Tobey Maguire, DiCaprio and Spielberg have tried, but even after the 90-year-old author does pass, anyone who is able to secure the rights would still have to navigate an impossible-to-capture tome, a disapproving fanbase and an intolerance for anything short of perfection.

"A Confederacy of Dunces" (yet to be filmed)

Like so many others on this list, "Dunces" needs to be read to be properly experienced. It's a trip into the quirky, annoying, wonderful mind of endearingly unemployed genius Ignatius J. Reilly in 1960s New Orleans, and it's virtually impossible to imagine on film. That hasn't stopped everyone from John Belushi and Steven Soderbergh to Richard Pryor, Will Ferrell and so many others from giving it a shot, however. Looking back, Ignatius' hatred of pop culture seems only appropriate, since he may never be a part of it.

"Don Quixote"

Technically, several versions of Miguel de Cervantes' 1605 Spanish Golden Age work of literature have been made over the decades. But far more notable are the "what could have beens," which include failed attempts by two of the greatest filmmakers of all time. Remember that Gilliam guy we mentioned earlier? Yep, his bad luck continued in the early part of this decade as he attempted to film an adaptation called "The Man Who Killed Don Quixote" with Johnny Depp, only to watch the movie fall apart and instead be documented as the tragically funny documentary "Lost in La Mancha." Decades earlier, the great Orson Welles began filming an adaptation in 1955 that would consume him for decades and never be completed. In the true spirit of Alonso Quixano's obsession with impossible quests, however, Gilliam announced this week that he had landed a new lead actor and will once again tilt at the "Quixote" windmill.